The preparation of biomolecules, such as peptides or oligonucleotides, and other organic compounds on a solid matrix is better performed using bifunctional spacer molecules known as linkers. One of the two reactive functionalities of a linker is permanently attached to a suitably functionalized resin, most often through a stable amide bond, while the growing molecule is temporarily linked at the other reactive position of the linker.
Although the majority of linkers rely on acidolysis for the release of the final molecule from the support, the use of different mechanisms (e.g. photolysis, fluoridolysis, and base-catalyzed Beta-elimination) has been exploited for the final cleavage.
Additionally biologically active molecules that selectively interact with specific cell types are useful for the delivery of radioactivity to target tissues. For example, radiolabelled peptides have significant potential for the delivery of radionuclides to tumours, infarcts, and infected tissues for diagnostic imaging and radiotherapy. 18F, with its half-life of approximately 110 minutes, is the positron-emitting nuclide of choice for many receptor imaging studies. Therefore, 18F-labelled bioactive peptides have great clinical potential because of their utility in PET to quantitatively detect and characterise a wide variety of diseases.
New blood vessels can be formed by two different mechanisms: vasculogenesis or angiogenesis. Angiogenesis is the formation of new blood vessels by branching from existing vessels. The primary stimulus for this process may be an inadequate supply of nutrients and oxygen (hypoxia) to cells in a tissue. The cells may respond by secreting angiogenic factors, of which there are many; one example, which is frequently referred to, is vascular endothelial growth factor (VEGF). These factors initiate the secretion of proteolytic enzymes that break down the proteins of the basement membrane, as well as inhibitors that limit the action of these potentially harmful enzymes. The other prominent effect of angiogenic factors is to cause endothelial cells to migrate and divide. Endothelial cells that are attached to the basement membrane, which forms a continuous sheet around blood vessels on the contralumenal side, do not undergo mitosis. The combined effect of loss of attachment and signals from the receptors for angiogenic factors is to cause the endothelial cells to move, multiply, and rearrange themselves, and finally to synthesise a basement membrane around the new vessels.
Angiogenesis is prominent in the growth and remodelling of tissues, including wound healing and inflammatory processes. Tumours must initiate angiogenesis when they reach millimeter size in order to keep up their rate of growth. Angiogenesis is accompanied by characteristic changes in endothelial cells and their environment. The surface of these cells is remodelled in preparation for migration, and cryptic structures are exposed where the basement membrane is degraded, in addition to the variety of proteins which are involved in effecting and controlling proteolysis. In the case of tumors, the resulting network of blood vessels is usually disorganised, with the formation of sharp kinks and also arteriovenous shunts. Inhibition of angiogenesis is also considered to be a promising strategy for antitumour therapy. The transformations accompanying angiogenesis are also very promising for diagnosis, one example being malignant disease, but the concept also shows great promise in inflammation and a variety of inflammation-related diseases, including atherosclerosis, the macrophages of early atherosclerotic lesions being potential sources of angiogenic factors.
Many ligands involved in cell adhesion contain the tripeptide sequence arginine-glycine-aspartic acid (ROD). The RGD sequence appears to act as a primary recognition site between the ligands presenting this sequence and receptors on the surface of cells. It is generally believed that secondary interactions between the ligand and receptor enhance the specificity of the interaction. These secondary interactions might take place between moieties of the ligand and receptor that are immediately adjacent to the ROD sequence or at sites that are distant from the ROD sequence.
The efficient targeting and imaging of integrin receptors associated with angiogenesis in vivo demands therefore a selective, high affinity RGD based vector that is chemically robust and stable. Furthermore, the route of excretion is an important factor when designing imaging agents in order to reduce problems with background.
WO 06/030291 relates to the use of peptide-based compounds as targeting vectors that bind to receptors associated with angiogenesis. Additionally, WO 2006/030291 describes peptide-based compounds having utility for diagnostic imaging which may be prepared rapidly. The present invention describes novel synthesis's of obtaining a modified Boc-protected aminoxy, —COOCH(CH3)3, PEG-6 linker. This PEG-6 linker can then be attached to a peptide based fragment to form a Boc-protected aminoxy peptide based compound. Thereafter the Boc-protected aminoxy peptide based compound is synthesized to obtain a radiolabelled peptide based compound that can be used in angiogenesis.
Discussion or citation of a reference herein shall not be construed as an admission that such reference is prior art to the present invention